To contain it, it has to be used in a magic show once every few weeks with a certain set of parameters (e.g., at least X number of audience members, show must be at least X minutes, etc.), or it poofs itself out of containment…and try to arrange the show itself.

It loves the stage, and would kill to be on it again and again.

I'm not sure whatever anything should be in the hat itself, but since there are only two rabbits SCPs, a bunny being one of the objects in the hat might be a possibility, but only if it works with the final concept.

A quick search shows that there aren't many SCPs relating to hats or stage magicians, but I want to make sure I don't accidentally make a SCP too similar to an existing one or one that isn't interesting.

So, intrigued?

EDIT: Actually, instead of being a rabbit in the hat, the hat used to be a rabbit.

A magician used a live rabbit for magic shows for years and years, until the rabbit died. The magician then used the rabbit's skin to create a hat and continue to use it.

For some reason or another (either known by the SCP Foundation or not), the hat remained sentient.

The SCP Foundation found the SCP after the SCP's efforts to force its owner to put on a show caused some deaths.

My first reaction is, "an over-the-top magician's hat that is actually magic." That said, I think this idea will all come down to how well you can execute it. You will also want to check out all of the pages tagged as performance.